Merge, premult, cameras, blacks and whites, explained with pictures you can move in your browser. Try it now without signing up, at your own pace.
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“A key is a mask, so more contrast is always better”
Crushing a key to pure black and white eats soft edges like hair and motion blur. Keep a soft key for the edge, a separate hard core key inside, and combine them with max.
“Screen is the best way to add light”
Nuke’s screen gives A+B−AB only when values are ≤ 1; above 1 it returns max(A,B), which clips HDR. For light, use plus.
“Matching blacks = raising lift in a Grade”
Grade lift pivots at 1, so it also pulls highlights down (lift 0.1 turns 4.5 into 4.15). Use a toe that only touches the darks.
“Add grain to every element along the way”
Grain goes on once, as the last node, per channel, blacks first; blue is usually the strongest.
“Any grade works fine on a premultiplied image”
Only pure multiplies are safe on premultiplied images. Lift, gamma and offset need unpremult → grade → premult, or the edges go wrong.
“CG needs pure black to look punchy”
Almost nothing in a real plate reaches 0. CG blacks follow depth: far things sit in haze, so their black is lifted and tinted.